The present invention relates generally to methods of and systems for testing voltage drops and current-carrying capacities of components of an electrical system, and more particularly to testing methods and systems that measure voltage drops in charging and starting components of the electrical system and compute the current carrying capacity and/or evaluate the condition of the components based thereon.
In an electrical system, loads and power sources are typically interconnected via wires, cables, bus bars, or other conductors. These conductors and the means of making connections therebetween may become loose, corroded, or damaged. It is therefore advantageous to test the conductors and the connections therebetween in electrical systems, especially those carrying large currents.
One example of such a system is an electrical system of an automobile or truck. Charging and starting portions of these electrical systems utilize very high currents, which are often as great as many hundreds of amps. Components of these electrical systems are frequently subjected to very harsh environments that include, for example, heat, moisture, large temperature changes, battery acid, and vibration. If the components become loose, corroded, or damaged, or are inadequate in size, their resistance will be too high for transmission of sufficient power from a source to a load of the electrical system. Higher resistances impede adequate current from flowing through the electrical system and create a voltage drop across the defective cables or bad connections, thereby reducing power to the load. In the charging portion of the electrical system high resistances can prevent necessary power from getting to a battery from the alternator. In the starting portion of the electrical system, adequate power may not be supplied to a starter from the battery.
A typical ohmmeter cannot be used to measure the resistance of cables and connections because the resistance in these components is typically very low (e.g., milliohms). To properly test the cables and the connections, voltage drops must be measured in the presence of a flowing current and calculations made based thereon using Ohm""s Law. In systems where the current varies, such as, for example, a charging portion, or in systems where the current is intermittent, such as, for example, a starting portion, steps must be taken to ensure that the voltage drop is measured during peak current flow. Voltage drop measurements under conditions of intermittent current have traditionally been tested by using a variable load tester having an auxiliary voltmeter. The variable load tester has typically been connected at the starter (or alternator) and auxiliary volt leads of the tester connected at the battery.
In such a procedure an operator applies and adjusts the current using the variable load tester. While current flows, the operator notes the voltage at the starter (or alternator), and also notes the voltage at the battery. The operator then subtracts one voltage from the other to obtain the voltage drop of the electrical system. If the voltage drop exceeds a specified amount (typically 0.5 volts), the electrical system is deemed problematic and the operator determines if the problem is in a positive leg or in a negative leg of the electrical system.
This determination is typically made by reconnecting the auxiliary volt leads to measure a voltage drop across the positive leg. The operator then applies and adjusts the load and notes the voltage across the positive leg. The voltage drop can not exceed one half of a maximal acceptable amount (i.e. 0.25 volts). A value exceeding one half of the maximal acceptable amount indicates a possible defect in the positive leg. To measure the voltage drop across a negative leg of the system, the auxiliary volt leads are moved to the negative leg. A load is applied and adjusted and the voltage drop across the negative leg is measured. A value exceeding one half of the maximal acceptable amount (i.e. 0.25 volts) indicates a possible defect in the negative leg.
Other variations of the aforementioned procedure, in which voltage drops are tested in an electrical system, have been attempted. For example, an inductive amp probe can be used to measure the current in the system and a variable load tester can be added to supplement the system load if needed. The operator is thereby allowed to connect the variable load tester at the battery; however, the operator is still required to perform multiple procedures and keep track of and subtract a series of voltages from one another. In addition, such approaches to testing voltage drops in an electrical system require the operator to perform multiple setups to completely test the positive and negative legs of the system.
Because voltage drop tests are so difficult to perform and require a significant amount of knowledge and skill by the operator, they are rarely performed. Often the battery, starter, or alternator is unnecessarily replaced, resulting in operations that fail to solve the underlying problem.
The present invention addresses these and other drawbacks by automatically determining current-carrying capacities and voltage drops in both positive and negative legs of an electrical system, after a setup procedure. In accordance with embodiments of the present invention, load leads of a testing device are connected at a starter (or alternator) in an electrical system of, for example, an automotive vehicle, while voltage leads of the testing device are connected at a battery of the electrical system. The testing device then applies a load of known resistance and measures a voltage at the load. Voltage drops in cables of the system are calculated by measuring a difference in voltage of two positive leads (a positive leg of the system) and two negative leads (a negative leg of the system). From the voltage across the load of known resistance, a current drawn by the testing device of the present invention is calculated from Ohm""s law. This current, along with the voltage drops in the positive and negative legs, is used to calculate a resistance in the two legs. The current that would produce a maximum allowable drop in the system and the percentage of the voltage drop in the positive and negative legs may then be calculated and displayed. The maximum current or the voltage drops can be compared to acceptable values and a xe2x80x9cpassxe2x80x9d or xe2x80x9cfailxe2x80x9d result can be given to the user.
In accordance with one embodiment of the present invention, a method of measuring voltage drops in an electrical system is described, in which a plurality of load leads are connected to, for example, a charging component or a starting component, of the electrical system. The plurality of load leads includes a positive load lead and a negative load lead, each coupled to a testing device. Additionally, a plurality of voltage leads are connected to a battery or system of the electrical system. The plurality of voltage leads also includes a positive voltage lead and a negative voltage lead, each of which are coupled to the testing device. A load of known resistance is applied to the electrical system by the testing device and a voltage is measured at the load. Then, a first voltage drop is measured between the positive load lead and the positive voltage lead and a second voltage drop is measured between the negative load lead and the negative voltage lead, wherein measurements of the first and second voltage drops are based, at least in part, on the voltage at the load.
In accordance with another embodiment of the present invention, a method of testing a magnetic switch circuit, which is coupled to a starter component in an electrical system, is described. The method begins with a step of first disconnecting the magnetic switch circuit from an xe2x80x9cSxe2x80x9d terminal of the starter component. A first positive lead of a plurality of load leads is connected to the xe2x80x9cSxe2x80x9d terminal. The plurality of load leads is also coupled to a testing device. A first negative lead of the plurality of load leads is connected to ground. At a second terminal of the starter component, a second positive lead of a plurality of voltage leads is connected. The plurality of voltage leads is also coupled to the testing device. A second negative lead from the plurality of voltage leads is connected to ground. The magnetic switch circuit is then energized and a first voltage drop, between the first positive lead and the first negative lead, and a second voltage drop, between the second positive lead and the second negative lead, is calculated. An indication of results obtained is provided, wherein the indication is based, at least in part, on the first and second voltage drops.
In accordance with yet another embodiment of the present invention, an apparatus for testing and measuring voltage drops in a positive and a negative leg of an electrical system is provided. The apparatus includes a plurality of load leads adapted to connect to a charging or starting component of the electrical system, wherein the plurality of load leads includes a positive load lead and a negative load lead, a plurality of voltage leads adapted to connect to a battery or system of the electrical system, wherein the plurality of voltage leads includes a positive voltage lead and a negative voltage lead; a means for applying a load of known resistance to the electrical system; a means for measuring a voltage at the load; and a means for measuring a first voltage drop between the positive load lead and the positive voltage lead, and a second voltage drop between the negative load lead and the negative voltage lead, wherein measurements of the first and second voltage drops are based, at least in part, on the voltage at the load.
In accordance with yet another embodiment of the present invention, an apparatus for testing a magnetic switch circuit coupled to a starter component, in an electrical system, is provided. The apparatus includes a means for disconnecting the magnetic switch circuit from an xe2x80x9cSxe2x80x9d terminal of the starter component; a first positive lead of a plurality of load leads adapted to connect to the xe2x80x9cSxe2x80x9d terminal, wherein the plurality of load leads is coupled to the tester; a first negative lead of the plurality of load leads adapted to connect to ground; a second positive lead from a plurality of voltage leads adapted to connect to a second terminal of the starter component, wherein the plurality of voltage leads is coupled to the tester, a second negative lead from the plurality of voltage leads adapted to connect to ground; a means for energizing the magnetic switch circuit; a means for calculating a first voltage drop between the first positive lead and the first negative lead and calculating a second voltage drop between the second positive lead and the second negative lead; and a first indicator, for providing a first indication of results obtained, wherein the first indication is based, at least in part, on the first and second voltage drops.